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A major breakthrough towards the quantum internet – Science et Avenir

Researchers have taken a key step towards a super-secure quantum internet by creating a rudimentary network for sharing information via triple teleportation, as they showed in a study on Wednesday.

The quantum internet, which should not see the light of day for ten years, will be a large-scale network connecting users through new applications and “cannot be achieved with a classical network,” explains Ronald Hanson of the University of Delft (AFP). Netherlands), co-author of this paper, published in the journal Nature.

The exchange of information will take place not in the form of classical bits – zeros and ones at the heart of calculations – but in the form of quantum bits (qubits).

These qubits use the laws of quantum physics that govern the world on an infinitesimal scale. One such property is entanglement, also called entanglement, a strange phenomenon in which two entangled particles behave the same regardless of the distance separating them: as if connected by an invisible thread, they are in the same state.

Thus, the state of the entangled qubit is shared with another, and their coordination is so perfect that one can speak of teleportation: in theory, any change in the properties of one instantly changes the properties of the other, even on the other side of the earth. .

Quantum bits can currently be transmitted over optical fibers, but teleportation remains limited: beyond a hundred kilometers, the signal is attenuated or even lost. If we want to maintain end-to-end entanglement, qubits must be directly linked in a quantum “chain”.

– Alice, Bob and Charlie –

This is a feat described in the study of nature, by which scientists introduced a relay to lengthen the communication range. Quantum Communication, which was limited to two actors usually named Alice and Bob, can now count on a third character, Charlie.

The experiment was carried out in two laboratories of the QuTech company, established jointly by the Delft University of Technology and the Dutch organization of applied sciences TNO.

The diamond-based qubits were placed in a chain consisting of three interconnections called “quantum knots”. Alice and Bob’s nodes are located in two labs a few meters apart and are connected by fiber optic cable, just like Bob is directly connected to Charlie. Alice and Charlie can’t talk to each other right now.

First, the researchers confused the physically connected nodes (the Alice-Bob pair and the Bob-Charlie pair). Then he used Bob as an intermediary and managed to confuse Alice and Charlie through the entanglement exchange process.

Even though they were not physically connected, the latter two were thus able to send messages to each other directly. The signal was also of excellent quality, without any loss – a problem, given the extreme instability of the quantum bit.

And this transmission could take place in the strictest secrecy, as required by quantum laws: with entanglement, any attempt to intercept or eavesdrop on the message automatically changes the qubits, destroying the message itself.

This first embryonic quantum teleportation network paves the way for large-scale interconnections: it proves on a laboratory scale the principle of a reliable quantum repeater – the famous Bob – that can be placed between two nodes 100 km apart, which increases signal strength.

The innovation, described in the journal Nature, represents a “victory for fundamental science” and “a real solution to take applied quantum physics to the next level,” the scientists greeted in a News and Opinion commentary published on the sidelines of the study. .

Speaking of the quantum internet, physicist Ronald Hanson describes a universe in which communications will be “ultra-secure” and the quantum computer will be available in the cloud with “the privacy of our data, guaranteed + by natural + laws of physics, by the network”. ultra-sensitive sensors…”.

Finding quantum network applications is “a field of research in itself,” adds the researcher, who hopes to see this new world born “in less than 20 years.”

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